I'm making an afghan and one row has me stumped. It reads........yo, k1, yo, p 3.......I get the yo k1, but isn't the yarn already over when you do a purl, so what's the point? The row has 4 yo's which increases the number of stitches by 4, but two are with knit stitches and 2 are with the purl. Hope this makes sense. Thanks for your help.

For yo's with purls you would do the opposite that you do with yo's with knits
With knits you bring the yarn to the front (like you were gonna purl the next stitch. And when you KNIT the stitch the yarn just goes over the top of the needle, you knit the next st and you have your yarn over.
With purls you would take the yarn to the back, (like yer gonna knit) insert the needle to purl and bring the yarn OVER the needle to the front and when yer done purling that st you have a yo.
Hopefully that makes sense.

I sometimes just loosely bring the yarn from the back over the needle to the front and purl, but it does make the hole smaller than the other way. Loose being the key word, I pull a little on the yarn as it lies in the needlle so it doesn't get pulled too tight when I purl the st.